Many devices utilize mercury in their operation, particularly in the field of electric lamps and lighting. Such devices include arc discharge lamps which typically employ mercury as one of the vaporizable components therein. See, for example, Waymouth, Electric Discharge Lamps, MIT Press 1971 for a description of the basic principles of such lamps.
In U.S. Pat. No. 4,379,252, (the '252 patent), the advantages of utilizing higher than normal levels of .sup.196 Hg in the Hg added to fluorescent lamps are described and include unexpectedly high efficiency gains in light output. The disclosure of this patent is hereby incorporated herein by reference.
The drawback of using this isotope lies in its high cost. For example, using conventional enrichment techniques, mercury which has been enhanced to contain about 35% of the .sup.196 Hg isotope can cost about $500 per milligram. While only sub-milligram quantities of this isotope need be added to a fluorescent lamp to afford beneficial results, economic realities always play a part in consumer products. Accordingly, it is easy to understand why more economical methods of obtaining this isotope continue to be sought.
Isotopically enriched mercury can be produced by a number of methods. One method involves photosensitized chemical reactions utilizing elemental mercury and various compounds. For example, the compounds HCl and O.sub.2 react with mercury atoms when the mercury atoms are excited by resonance radiation, in particular, 2537 .ANG. radiation produced in a Hg (.sup.3 P - .sup.1 S.sub.o) transition generating isotopically selective reactions. Thus, the Hg compound formed contains Hg enriched in a particular isotope, and the Hg must be separated from the compound into its liquid or free state (i.e., elemental Hg)) in order to recover the isotopically enriched metal.
As described above, anhydrous HCl is used in the photochemical isotope separation of .sup.196 Hg. However, only a small fraction of the HCl present is actually utilized, the rest is deposited as a solid effluent, typically in liquid nitrogen cold traps along with effluent mercury. To recover the mercury, the solid HCl is allowed to liquefy and then vaporize; however, the HCl vapor must be disposed of. Previously this was done by simply exhausting the HCl to the outside air. This can be hazardous, especially in the vicinity of the outside exhaust vent, and particularly during periods of precipitation [e.g., concentrated acid rain].
A standard method of eliminating this problem is to utilize one or more gas scrubbers in series with the ventilation system which removes the anhydrous HCl from the exhaust air. This produces aqueous HCl, which can be neutralized and more easily disposed of. However, gas scrubbers of this type are large and require sophisticated control systems for their operation.
The present invention offers a simple solution to the problem of dealing with anhydrous HCl remaining in mercury enrichment processing.